Production of crimped yarns



United States Patent 3 9 9 Claims. (Cl. 8-1301) The invention relates to the production of crimped yarns based upon polyolefines, and more especially based upon polypropylene.

The yarns obtained from synthetic polymers such as polyamides, polyesters and polyolefines possess excellent properties, such as high tensile strength and rapid drying, but give smooth fabrics of high lustre which are not suitable for all applications.

Many processes have already been proposed for imparting to such continuous synthetic yarns a handle and an appearance comparable to those of wool. The commonest process consists in twisting the yarns, setting the twist and untwi-sting, these operations being carried out in separate successive stages in accordance with the conventional method, or in one stage in accordance with the false-twist method. In another method, the yarns are packed in a box (a so-called s-tufiing box) and subjected to a thermal treatment. The yarns may also be passed over .a heated knife-edge under a light tension.

The crimped yarns thus obtained, although they can fairly readily be used for the manufacture of knitwear and stockinet, are difficult to weave by the conventional methods, owing to their very high elasticity. Moreover, it is found that when polyolefine yarns textured by these methods are kept on bobbins, the stability of the crimp is not at all good.

The present invention relates to a process for producing yarns based on polyolefines, and more especially on polypropylene, which have a non-helical crimp having no loops, and which are not attended by the aforesaid disadvantages. The crimp is irregularly disposed along the yarn, i.e. the undulations are in dilferent planes and have an irregular period. Nevertheless, as shown in the examples, below, the amplitude of the crimp may be very regular.

The process according to the present invention consists in subjecting a yarn based upon polyolefines, at least partly formed of stretched continuous filaments, to the action of a swelling agent in the form of vapour or of a mist at a temperature close to the boiling temperature of the said agent, for a time less than 20 seconds.

Preferably, the operation is continuously carried out by passing the yarn through a treatment chamber containing a swelling agent in the form of vapour or of a mist, at a temperature close to the boiling temperature of the said swelling agent.

If it is desired that the crimp shall be substantially resistant to tensioning of the yarn, the treatment with the swelling agent is followed by a heat treatment.

The swelling agent employed for carrying out this process may be chosen from the aromatic hydrocarbons (more especially those of the benzene series, such as toluene), the hydroaromatic hydrocarbons (such as cyclohexane, decalin or tetralin), or the chlorinated aliphatic or aromatic hydrocarbons (such as carbon tetrachloride, dichloroethane, trichloroethylene, tetrachloroethylene and chlorobenzene) The process is particularly suitable for the production of a crimped yarn based upon polypropylene. The yarn obtained is light and has high bulk and high covering power, because the filaments are maintained in spaced relation to one another by undulations situated in different planes and irregularly distributed over the entire Patented Mar. 8, 1966 length. The crimp obtained is between 20% and depending upon the operating conditions, but the most attractive yarns are those whose crimp amount to 30- 45%. The percentage crimp is given by the formula:

Ll XIOO of which the symbols have the following meanings:

L=-1ength of the uncrimped yarn, l=length of the yarn in the crimped state.

The apparatus employed in carrying out the process of the invention comprises mainly:

A feed roll,

A chamber for the treatment of the yarn, filled with the vapour of the swelling agent or a mist at a temperature close to the boiling temperature of the agent, and

A take-up roll.

The yarn may bewound at a speed of some tens of metres per minute and is supplied at a speed 20l00% higher. The yarn is maintained under a negligible tension. The duration and the length of the travel through the treatment chamber may be varied. For a polypropylene yarn treated with trichloroethylene vapours, the residence time is preferably between 0.8 and 7 seconds.

The crimp appears spontaneously in the filaments of the yarn in the chamber without any subsequent .treatment being necessary. However, it is advantageous to subject the yarn to a steam treatment in an oven.

The intensity and the regularity of the amplitude of the crimp may be influenced by the spinning conditions, the yarn stretching conditions, the twist of the yarn, the prior treatments which the yarn may have undergone, i.e. twisting, twist-setting and untwisting (under conditions unrelated to the normal conditions for the production of a high-bulk yarn), thermal treatment, steam treatment, etc. Thus, while the treatment of an untwisted yarn results in a highly irregular, more or less random crimping, which is very desirable for some purposes, the yarn may be induced to take a crimp having a more regular amplitude either by applying a comparatively low twist, say 50 turns or so per metre, and crimping it in the twisted state or by applying a twist in one direction, e.g. 200 turns per metre but in any casenot a high twist such as is used in the production of high bulk yarn, then setting and unt-wisting before applying the crimping treatment characteristic of the invention.

The invention is illustrated in the following examples:

Example I A so-called isotactic polypropylene yarn of 600 denier, 138 filaments, which has been drawn to an extent of 5.5 times, is continuously passed through a treatment chamber consisting of a vertical cylindrical tube whose lower end communicates with a boiler containing boiling trichloroethylene, and whose upper end is open and is cooled by a cooler through which water is circulated. The yarn enters the chamber by way of its upper end, travels along a path in the form of a very acute V using a guide at the bottom of the V and leaves the chamber through the same orifice. It is fed at a speed of 40 metres per minute and wound up at 25 metres per minute. It travels along a path of 60 cm. in the trichloroethylene vapours, which corresponds to a period of immersion in the vapours of about 1 second.

The yarn collected on the winding bobbin has a crimp of 37.5% and a denier of 960.

The yarn is thereafter subjected to a steam treatment in an oven for an hour at 140 C. The crimped yarn thus obtained can be used for making undergarments.

boiling trichloroethylene.

3 Example II A polypropylene yarn identical with that of Example I is continuously treated under the same conditions as in the said example. Only the length of the passage through the trichloroethylene vapours differs: it is 110 cm. The yarn is crimped to the extent of 37.5% like that of Example I, but it has a finer and more compact curl.

Example III A polypropylene yarn of 600 denier and 138 filaments is pretwisted with 50 Z-turns per metre. It is caused to travel continuously along a path of 110 cm. in the trichloroethylene vapours, the feed rate being 45 metres per minute and the wind-up speed 25 metres per minute.

A yarn is obtained whose crimp has a more regular amplitude than in Example I, and whose crimp is 44.4%.

The yarn, when steam-treated for one hour at 140 C., is particularly suitable for the production of knitted articles.

Example IV A polypropylene yarn of 600 denier and 156 filaments is pretwisted with 200 Z-turns per metre, set in an oven at 90 C. for 2 hours, untwisted by applying 200 S-turns per metre, and then treated for about 1 second with trichloroethylene vapours.

The treatment is carried out in a horizontal chamber having the shape of a parallelepiped whose lower portion is heated by an electrical resistance and which contains The vapours of the solvent fill the chamber. These vapours are prevented from escaping into the atmosphere through the open upper end by means of coolers disposed on the upper part of the side walls and cooled by circulating water.

The yarn enters the end of the treatment chamber by way of a slot and travels therein along a rectilinear horizontal path and leaves it at the other end.

A yarn of 960 denier, having a very regular crimped effect and a crimp of 37.5% is obtained, the crimp being very regular in amplitude.

Example V A polypropylene yarn of 630 denier and 117 filaments is tristed with 20 Z-turns per metre, and heat-treated for one hour at 100 C.

It is continuously passed through cyclohexane vapours at a feed speed of 21 metres per minute and a take-up speed of 15 metres per minute. The length of its travel in the treatment chamber is 110 cm.

The yarn obtained has a crimp of 40%, the crimp being fine and regular in amplitude.

I claim:

1. Process for the production of a crimped yarn, comprising subjecting a polyolefine yarn, at least some of whose filaments have been stretched or drawn, and which is substantially free from swelling agents for the polyolefine, to the action of an atmosphere charged with a swelling agent for the polyolefine at a temperature near the boiling point of the swelling agent and for a period up to 20 seconds.

2. Process for the production of a crimped yarn, comprising subjecting a polypropylene yarn, at least some of whose filaments have been stretched or drawn, and which is substantially free from swelling agents for the polypropylene, to the action of an atmosphere charged with a swelling agent for the polypropylene at a temperature near the boiling point of the swelling agent and for a period up to 20 seconds. 7

3. Process for the production of a crimped yarn, comprising subjecting an isotactic polypropylene yarn, at least some of whose filaments have been stretched or drawn, and which is substantially free from swelling agents for the polypropylene, to the action of an atmosphere charged with trichloroethylene at a temperature near the boiling point of the trichloroethylene and for a period up to 20 seconds.

4. Process according to claim 2, wherein the yarn is subsequently heat-treated.

5. Process according to claim 3, wherein the yarn is subsequently heat-treated.

6. Process for the production of a crimped polypropylene yarn, comprising subjecting an isotactic polypropylene yarn, whose filaments have been stretched or drawn, and which is substantially free from swelling agents for the polypropylene, to the action of an atmosphere charged with a swelling agent for the polypropylene and at a temperature near the boiling point of the swelling agent for a period up to 20 seconds, the yarn being under such a low tension that it crimps during the treatment and the swelling agent being selected from the group consisting of aromatic and hydroaromatic hydrocarbons and chlorinated aliphatic and aromatic hydrocarbons.

7. Process for the production of a crimped polypropylene yarn, comprising continuously feeding an isotactic polypropylene yarn, whose filaments have been stretched or drawn, and which is substantially free from swelling agents for the polypropylene, into a swelling zone where it is subjected for a period up to 20 seconds to the action of an atmosphere charged with a swelling agent for the polypropylene and at a temperature near the boiling point of the swelling agent and continuously withdrawing the yarn from the swelling zone at a speed 3045% lower than the feed speed whereby a crimp within said percentage range is imparted to the yarn.

8. Process according to claim 6, wherein the yarn is subsequently heat-treated to fix the crimp.

9. Process according to claim 7, wherein the yarn is subsequently heat-treated to fix the crimp.

References Cited by the Examiner UNITED STATES PATENTS DONALD W. PARKER, Primary Examiner. MERVIN STEIN, Examiner. 

1. PROCESS FOR THE PRODUTION OF A CRIMPED YARN, COMPRISING SUBJECTING APOLYOLEFINE YARN, AT LEAST SOME OF WHOSE FILAMENTS HAVE BEEN STRETCHED OR DRAWN, AND WHICH IS SUBSTANTIALLY FREE FROM SWELLING AGENTS FOR THE POLYOLEFINE, TO THE ACTION OF AN ATMOSPHERE CHARGED WITH A SWELLING AGENT FOR THE POLYOLEFINE AT A TEMPERATURE NEAR THE BOILING POINT OF THE SWELLING AGENT AND FOR A PERIOD UP TO 20 SECONDS. 